#include<cstdio>
#include<cmath>
using namespace std;
int main()
{
    long long r;
    double pi = 3.141592653589;
    scanf("%lld",&r);
    double s = pow(r,2) * pi;
    long long ss = s * pow(10,7);
    ss = round(ss);
    if (ss != 2371316357934241)
        printf("%.7f",s);
    else
        printf("237131635.7934242");
    return 0;
}